A sewing machine of a similar construction is described in U.S. Pat. No. 2,482,079. The spreader has the function of pulling the thread out laterally as it issues from the region of the looper tip and as it runs upward to the stitch hole in such a way that the descending needle moves between the looper and the extracted lower thread. This process is generally referred to as tagging, i.e. entrance of the needle tip into a triangle formed by two sides of the upper thread and by the lower thread.
The drive of the connecting rod which carries the spreader is arranged perpendicular to the swinging direction of the looper and it is axially displaceable and parallel to the main shaft of the machine. The drive occurs in the known sewing machine from an eccentric secured on a shaft in drive connection with the arm shaft. The drive proceeds to a needle bearing through an eccentric rod in whose output end, designed as socket, a ball-shaped sleeve is mounted. A radial pin is guided through a bore of the sleeve and it is oriented parallel to the connecting rod and secured in a rocking shaft extending perpendicular to the connecting rod. The swinging motions imparted to the rocking shaft are transmitted to the connecting rod with a spreader via a crank arm secured on it. The crank arm has a radial pin which is guided in a bore of a cylindrical connecting pin for displacement in a fork head secured on the connecting rod. Thus, the connecting rod executes swinging motions perpendicular to the swinging direction of the looper.
Due to the oblique position of the radial pin relative to the axis of rotation of the drive eccentric in the ball-and-socket joint on the output side of the eccentric rod, which obliquity changes continually with the swinging motions of the rocking shaft, considerable transverse forces occur. The forces act above all on the needle bearing of the drive eccentric and cause intensive heating and high wear, necessitating frequent replacement repairs.